Valves are commonly used in process control systems to control the flow of process fluids. Sliding stem valves (e.g., a gate valve, a globe valve, a diaphragm valve, a pinch valve, etc.) typically have a closure member (e.g., a valve plug) disposed in a fluid path. A valve stem operatively couples the closure member to an actuator that moves the closure member between an open position and a closed position to allow or restrict fluid flow between an inlet and an outlet of the valve. Additionally, to provide a desired and/or to achieve certain flow characteristics of the fluid, valves often employ a cage that interposes in the path of fluid flow between the inlet and the outlet of the valve. A cage can reduce capacity flow, attenuate noise, and/or reduce or eliminate cavitation.
Typically, the size of the valve, industrial process conditions such as operational temperatures (e.g., temperatures between −100° F. and 450° F., temperatures greater than 450° F., etc.) of the process fluids are used to determine the type of valve or valve components that may be used such as, for example, the types of seals that may be used to effect a seal between a cage, a valve seat, a valve body and/or a closure member.
Further, the type of seals that are used usually determines the valve seat/seal configuration. For example, to provide a seal between a valve seat and a valve body, a seal composed of, for example, polytetrafluoroethylene (e.g., PTFE or Teflon®) is typically disposed between a valve seat and a valve body for process fluids having temperatures less than 450° F. For example, the seal may be disposed within an annular recess formed around an outer peripheral surface of the valve seat. The valve seat is coupled to a cage (e.g., via threads), which suspends the valve seat within a fluid flow path of the valve body when the cage is coupled to the valve body. The seal prevents fluid leakage between the valve body and the valve seat. However, process fluids having temperatures greater than 450° F. may cause a seal composed of polytetrafluoroethylene to extrude or fail.
For process fluids having temperatures greater than 450° F., a valve seat/seal configuration includes a gasket disposed between the valve seat and the valve body. However, such a valve seat/seal configuration requires the valve seat to be fastened (e.g., bolted) to the valve body. Thus, a valve seat/seal configuration of a valve for use with process temperatures greater than 450° F. uses a valve body that is different than a body of a valve having a valve seat/seal configuration for use with process fluid having temperatures less than 450° F.